Chapter 5/6 Test Questions (Midterm)
Energy Units
J
Work units
Joules (J) (a newton meter)
Kinetic Energy Formula
Kinetic Energy = 1/2 mass x velocity^2
Momentum formula
Momentum = mass x velocity
Impulse units
Ns
Potential Energy Formula
Potential Energy = mass x acceleration due to gravity x height
Work Formulas
Work = Force x distance Work = mass x acceleration x distance
Work energy theorem
Work = the change in energy
Exert 1 N for a distance of 1 m in 1 s and you deliver a power of . . . a) 1 W b) 2 W c) 1/3W d) 3 W e) none of these
a) 1 W
A machine puts out 100 W of power for every 1000 W put into it. The efficiency of the machine is . . . a) 10% b) 50% c) 90% d) 110 % e) none of these
a) 10%
A 4-kg ball has a momentum of 12 kgm/s. What is the ball's speed? a) 3 m/s b) 4 m/s c) 12 m/s d) 48 m/s e) none of these
a) 3 m/s
Which of the following is NOT a true statement about energy? a) Energy is created by putting an object in motion b) If an object is able to do work it has energy c) Energy causes motion d) Energy can change easily from one form to another
a) Energy is created by putting an object in motion
The work output of a machine compared to the work input is the ____ of the machine. a) efficiency b) power c) effort d) resistance
a) efficiency
A force caused by two surfaces rubbing together that opposes motion is called ____. a) friction b) gravity c) Newton d) velocity
a) friction
A heavy truck and a small car rolling down a hill at the same speed are forced to stop in the same amount of time. Compared to the force that stops the car, the force needed to stop the truck is . . . a) greater b) smaller c) the same
a) greater
A clerk can lift containers a vertical distance of 1 m or can roll them up a 2-m-long ramp to the same elevation. With the ram, the applied force required is about . . . a) half as much b) twice as much c) the same
a) half as much
The amount of work done when a force of one Newton acts through a distance of one meter is equal to a ____. a) joule b) kilogram c) Celsius degree d) calorie
a) joule
A bar that is free to pivot about a mixed point is a ___. a) lever b) wedge c) fulcrum d) ram
a) lever
An object that has kinetic energy must be . . . a) moving b) falling c) at an elevated position d) at rest e) none of these
a) moving
If you push for an hour against a stationary wall, you do no work . . . a) on the wall b) at all c) both of these d) none of these
a) on the wall
According to the impulse-momentum equation Ft= change in (mv), a bungee jumper in falls momentum which is reduced by the force F exerted by the bungee cord. If m is the mass of the jumper, then v in the equation is the speed of the . . . a) jumper b) cord c) both of these d) none of these
a) the jumper
If you push an object just as far while applying twice the force, you do . . . a) twice as much work b) four times as much work c) the same amount of work
a) twice as much work
If you push an object twice as far while applying the same force, you do . . . a) twice as much work b) four times as much work c) the same amount of work
a) twice as much work
mechanical advantage units
always a percent, no units
It takes 40 J to push a large box 4 m across the floor. Assuming the push is in the same direction as the move, what is the magnitude of the force on the box? a) 4 N b) 10 N c) 40 N d) 160 N e) none of these
b) 10 N
A ball is moving at 4 m/s and has a momentum of 48 kgm/s. What is the ball's mass? a) 4 kg b) 12 kg c) 48 kg d) 192 kg e) none of these
b) 12 kg
In raising a 5000-N piano with a pulley system , it is noted that for every 1 m of rope pulled down the piano rises 0.1m. Ideally, this means that the force needed to lift it is about . . . a) 50 Newtons b) 500 Newtons c) 5000 Newtons d) there is not enough information given to estimate
b) 500 Newtons
Which of the following has the larges momentum relative to the Earth? a) a tightrope walker across Niagara Falls b) a pickup truck speeding along a highway c) a Mack truck parked in a parking lot d) the science building e) a dog running down the street
b) a pickup truck speeding along a highway
Energy is the . . . a) force of an object b) capacity to do work c) measurement of power d) speed of gravity
b) capacity to do work
A freight train rolls along a track with considerable momentum. If it rolls at the same speed but has twice as much mass, its momentum is . . . a) zero b) doubled c) quadrupled d) unchanged
b) doubled
A winding mountain road is an example of what kind of simple machine? a) lever b) inclined plane c) wheel and axle d) a pulley
b) inclined plane
Which of the following CANNOT be done by a simple machine? a) change the direction of force b) increase the amount of work done c) decrease the amount of time it takes to do the work d) transfer energy from one location to another
b) increase the amount of work done
As an object's potential energy decreases, its kinetic energy _____. a) decreases b) increases c) stays the same d) is halved
b) increases
Momentum is expressed in units of ____. a) kgm b) kgm/s c) N d) m/s/s
b) kgm/s
A job is done slowly, while an identical job is done quickly. Both jobs require the same amount of work, but different amounts of . . . a) energy b) power c) both of these d) none of these
b) power
Which of the following groups of simple machines represent variations of the lever? a) pulley, inclined plane, and wedge b) pulley, wheel and axle c) pulley wedge and screw d) wedge, screw, and wheel and axle
b) pulley, wheel and axle
An inclined plane wrapped around a cylindrical post is a _____. a) wedge b) screw c) block and table d) lever
b) screw
It is correct to say that impulse is equal to . . . a) momentum b) the change in momentum c) the force multiplied by the distance the force acts d) all of these e) none of these
b) the change in momentum
The difference between impulse and impact force involves the . . . a) distance the force acts b) time the force acts c) difference between acceleration and velocity d) mass and its effect on resisting a change in momentum
b) time the force acts
An object is raised above the ground gaining a certain amount of potential energy. IF the same object is raised twice as high, it gains . . . a) four times as much potential energy b) twice as much potential energy c) neither of these
b) twice as much potential energy
Three of the following simple machines are basically the same. Choose the one that DOES NOT belong with the group. a) pulley b) wedge c) lever d) wheel and axle
b) wedge
Exert 100 J in 50 s and your power output is . . . a) 1/4 W b) 1/2 W c) 2 W d) 4 W e) more than 4 W
c) 2 W
Two simple machines that are apart of a bicycle are ___. a) an inclined plane and a wedge b) an inclined plane and a lever c) a gear and a wheel and axle d) a wheel and axle and an inclined plane
c) a gear and a wheel and axle
When you jump from an elevated position you usually bend your knees upon reaching the ground. By doing this, the time of impact is about 10 times more than for a stiff-legged hanging. In this way the average force you body experiences in reduced by . . . a) less than 10 times b) more than 10 times c) about 10 times
c) about 10 times
Which requires more work: lifting a 50-kg sack vertically 2 m or lifting a 25-kg sack vertically 4 m? a) lifting the 50-kg sack b) lifting the 25-kg sack c) both require the same amount of work
c) both require the same amount of work
Consider driving into a massive concrete wall with no "give", versus having a head on collision at the same speed with an identical car moving toward you with the same speed. It would be more damaging to hit . . . a) car b) wall c) both the same
c) both the same
You're driving down the highway and a bug spatters into your windshield. Which undergoes the greater change in momentum? a) the bug b) your car c) both the same
c) both the same
According to the law of conservation of energy, when a book falls to the floor . . . a) energy is created b) energy is destroyed c) energy is changed from one form to another d) there is no change in the form of energy
c) energy is changed from one form to another
The amount of kinetic energy a moving object has depends on its . . . a) weight and the distance lifted b) Weight and force c) mass and speed d) speed and motion
c) mass and speed
Energy stored in an object as a result of a change in position is called . . . a) kinetic energy b) solar energy c) potential energy d) conservation of energy
c) potential energy
The rate at which work is done is ______. a) efficiency b) effort time c) power d) force
c) power
A rifle recoils from firing a bullet. The speed of the rifle's recoil is small because the . . . a) force against the rifle is smaller than against the bullet b) momentum is mainly concentrated in the bullet c) rifle has more mass than the bullet d) momentum of the rifle is smaller
c) rifle has more mass than the bullet
In order to catch the ball, a baseball player extends the hand forward before impact with the ball and then lets it ride backward in the direction of the ball's motion upon impact. Doing this reduces the force of impact on the players hand principally because the . . . a) force of impact is reduced b) relative velocity is less c) time of impact is increased d) time of impact is decreased e) none of these
c) time of impact is increased
A 1000-kg car and 2000-kg car are hoisted the same distance in a gas station. Raising the more massive car requires . . . a) less work b) as much work c) twice as much work d) four times as much work e) more than four times as much work
c) twice as much work
If you do work on an object in half the time, your power output is . . . a) half the usual power output b) the same power output c) twice the power output
c) twice the power output
The unit of power is the ____. a) joule b) Newton c) Watt d) m/s/s
c) watt
A TV set is pushed a distance of 2 m with a force of 20 N that is in the same direction as the set moves. How much work is done on the set? a) 2 J b) 10 J c) 20 J d) 40 J e) 80 J
d) 40 J
Two inclined planes put together form a simple machine called _____. a) a screw b) an effort arm c) a lever d) a wedge
d) a wedge
Strictly speaking, if any electrical device in your car is turned on (such as an air conditioner, headlights, or even a radio), more gasoline is burned by the engine. This statement is . . . a) totally false b) true only if the car's engine is running c) true only if the car's engine is stopped d) always true e) none of these
d) always true
A system of pulleys designed traduce the effort force is called a ____. a) simple pulley b) fixed pulley c) movable pulley d) block and tackle
d) block and table
An object that has potential energy may have this energy because of its . . . a) speed b) acceleration c) momentum d) location e) none of these
d) location
When two objects collide, the momentum of the pair after the collision is explained by ____. a) Newton's first law of motion b) Newton's second law of motion c) Newton's third law of motion d) the conservation of momentum
d) the conservation of momentum
When a care is braked to stop, its kinetic energy is transformed to . . . a) stopping energy b) potential energy c) energy of motion d) energy of rest e) heat
e) heat (like friction)
The fixed point at which a lever is supported is called the _____.
fulcrum
Conservation of Momentum units
kgm/s
momentum units
kgm/s
The device that changes the size or direction of a force is called a ______.
machine
efficiency units
no units, always a percent
mechanical advantage
output force/input force
When a force causes something to move, it does _____.
work
Power formula
work done/ time
Law of conservation of momentum
(total mass x velocity) before collision = (total mass x velocity) after collision
review the diagram of the 1st class lever answer: :)
:)
Review first, second, and third class levers answer: :p
:p
Efficiency formula
Efficiency = work done/ energy used
Impulse formula
Force x time = the change in mass x velocity
